Dielectric frame beam waveguide

ABSTRACT

An iterative or beam waveguide consisting of several guide elements which are identical, parallel, inter-equidistant and coaxial to the beam&#39;&#39;s axis, characterized by the fact that it is made up of several identical cross sections realized in dielectric material, with each pair of cross sections having a function equivalent to that of a resonator formed by a pair of flat parallel reflectors symmetrically placed, with each reflector having a stepped edge and with the dimensions of said cross sections having outside measurements little greater than the beam&#39;&#39;s, the beam being in said cross sections, which are placed at equal distances from each other, the distances being equal to those separating the cross sections&#39;&#39; equivalent resonators&#39;&#39; reflectors, every cross section, which carries out a function equivalent to that of the resonators&#39;&#39; reflectors&#39;&#39; peripheral step corresponding to the cross section, creating a phase jump having a transverse area width large enough to allow reconstructing the original size of the beam modified, as it were, during passage from one cross section to the next, and having a thickness computed in a way to correspond to minimum loss or attenuation, which can be suffered by a beam-type wave.

ass-911. H

AU 255 EX Checcacci et al.

[541 DIELECTRIC FRAME BEAM WAVEGUIDE [75] Inventors: Pier Francesco Checclcci; An-

namaria Scheggi, both of Firenze, Italy [73] Assignee: Consiglio Nazionnle Delle Richerche,

Roma, Italy [22] Filed: Sept. 23, 1971 [21] Appl. No.: 183,046

Primary Examiner-John K. Corbin Attorney Ernest F. Marmorek [111 3,733,114 51 May 15,1973

[57] ABSTRACT An iterative or beam waveguide consisting of several guide elements which are identical, parallel, interequidistant and coaxial to the beams axis, characterized by the fact that it is made up of several identical cross sections realized in dielectric material, with each pair of cross sections having a function equivalent to that of a resonator formed by a pair of flat parallel reflectors symmetrically placed, with each reflector having a stepped edge and with the dimensions of said cross sections having outside measurements little greater than the beams, the beam being in said cross sections, which are placed at equal distances from each other, the distances being equal to those separating the cross sections equivalent resonators reflectors, every cross section, which carries out a function equivalent to that of the resonators reflectors peripheral step corresponding to the cross section, creating a phase jump having a transverse area width large enough to allow reconstructing the original size of the beam modified, as it were, during passage from one cross section to the next, and having a thickness computed in a way to correspond to minimum loss or attenuation, which can be suffered by a beam-type wave.

5 Claims, 12 Drawing Figures SHEET 3 OF 3 1 DIELECTRIC FRAME BEAM WAVEGUIDE The invention described below concerns a beam waveguide of iterative type. The waveguide consists of several cross sections realized in dielectric material. The cross sections are aligned at equal distances and placed coaxially to a wave transmitter, or similar conventional-type instrument. Each pair of adjacent cross sections functions as a device equivalent to a resonator having flat reflectors with stepped peripheral edge.

The invention involves, moreover, two variants:

the first, for executing directional coupling;

the second, for optimal radiating and receiving of wide-end-tipped antennas.

Relative to the invention, drawings attached at the end of this description format a few conventional types of waveguides and various makeups for realizing iterative guides.

Said conventional devices have been illustrated to better evidence, through comparison with alreadyknown types, the innovative characteristics of the waveguide pertinent to the invention being described here. Each waveguide represented, moreover, is related to the corresponding resonator's format since, as mentioned above, each element pair making up the waveguide can be considered functionally equivalent to a resonator.

FIGS. 1a and lb, and 211 respectively form in axial section two conventional-type waveguides and their relatively corresponding resonators.

FIGS. 34 and 3b, 4a and 4b likewise form phase-step iterative guides and their relatively corresponding resonators.

FIG. 5 forms in axial section a makeup for simple cross section execution.

FIGS. 6 and 7 form, in angular view, an iterative guide with cylindrical and one with rectangular cross sections.

FIG. 8 forms in axial section a double waveguide device for executing directional coupling.

Note, in reference to the above figures, that the waveguide is related to an already-known-type of wave transmitter. The latter device is not illustrated and described, but is indicated generically with a 1, while the beam 5 axis is indicated with an X and coincides with the waveguide's axis.

Note also that the iterative beam waveguide has, like ordinary types of waveguides, a periodic structure to permit the transport of energy. The iterative beam waveguide differs from ordinary waveguides, however, in that it has an open structure along which there is variation in field distribution, although the field configuration repeats itself periodically on the elements making up the structure. Precisely then, the transport of energy is carried out by replacing on each element the beam coming from the preceding one, each new element involved in the energy transport being opened through diffraction.

Beams propagated in the above manner are called iterative beams and their fields are structurally open, giving them harmonic modes which satisfy the same conditions of mutual perpendicularity relative to the modes of ordinary guides. To be guided, harmonic modes require the same type of periodic elements and present diverse attenuation. The beam guide utilize the lowest attenuation mode.

The dimensions of the beams transversal section are generally very large relative to the wave length. Consequently, the beam-type guide is especially appropriate for milli and sub-millimeter bands, wherein metallic waveguide construction and functioning are extremely difficult.

The two most typical examples of the abovementioned type of beam guide are:

the guide made up of a sequence of identical irides 2 (FIG. la), drawn into two opaque screens, at d equidistance, with each pair of two such irides being equivalent (FIG. lb) to a resonator formed by two flat reflectors 3, of 2a diameter equal to the central opening of each iride 2 and placed at d distance; the guide made up of a periodic series of lenses 4, in dielectric material, placed at equal distances d and having a 20 diameter, each pair of lenses 4 being equivalent to a resonator (FIG. 2b) with concave reflectors 5 of 2a diameter and placed at d distance.

For the guide using irides (FIG. la), the reconstruction of the beam (indicated by dotted line) on each iride 2 is related to the reduction the irides introduce in the opening of the beam itself. For the guide using lenses (FIG. Zn), on the other hand, phase modification (in the beams section) occurs, and does so relative to the passing through of each lenses 4.

The two above guide systems losses (attenuation) are due to: 1

either diffraction on the part of the single elements making up the guides structure (limited opening) or losses inherent in the elements themselves, such as difi'usion, so-called scattering," reflection, etc.

Note again that study of this type of iterative guides modes and losses can be done by studying the modes and losses of the relevant open resonators, the latter using flat reflectors 3 (FIG. lb) or curved reflectors 5 (FIG. 2b) and lending themselves to evident analogy. These resonators can in efi'ect be considered as said guides resonant sections (FIG. la and FIG. 2a) and thereby present identical mode systems.

Thus formed is the scope of the invention being described here: an iterative or beam guide which reproduces the functioning and characteristics of a particular type of resonator. Said resonator, more precisely, is made up of flat parallel reflectors 6 and 7, respectively (FIG. 3b and FIG. 4b). These reflectors have in turn peripheral edges 6a and 7a. The edges themselves are stepped at a width of L, and the step thickness has an absolute value equal to 6. The step offset can jut negatively (FIG. 3b) or positively (FIG. 4b) relative to the plane of a given reflector, and reflectors having stepped edges 6, 6a or 7, 7a are placed symmetrically to one another.

The above-mentioned resonators, made up of stepped peripheral-edge flat reflectors, have marked loss properties. These losses vary periodically in function with the thickness of each reflectors edge, said thickness having a N2 and 8 period for negative and positive values. Once, consequently, a value for losses is fixed, one can choose the most appropriate thickness from among those presenting such losses.

The iterative guide, equivalent to the resonator having the format type illustrated in FIG. 3b or FIG. 4b, is made up of irides, drawn into opaque screens 8, with central openings of 20 diameter. The function of the edges 6a or 7a is done by means suited to obtaining an equivalent phase jump, the latter being attained as shown in FIG. 34, wherein the irides opening is partially covered with a slide 9 made of dielectric material having an appropriate thickness. The slide itself is sized to allow passage of a beam of width 1 between the edge of the irides opening and the edge of the very slide. Taking account of the periodic nature of the losses outlined above, the same phase jump which corresponds to the like value of the losses can be obtained through use of a structure complementary to that shown in FIG. 3a. Said structure utilizes a simple cross section 11 of dielectric material (FIG. 4a) applied along the edge of the Za-diameter opening of each iride 8, the cross sections transverse having the width 1 and the thickness 5'. The phase jump, or 8' thickness equivalent to the 8 thickness of the step of the reflectors stepped at 7 pertinent to the relative resonator, is chosen so as to give minimum loss. Under these conditions, the field is practically zero at the edges of the reflectors 6 or 7 or, alternatively, at the edge of the opening of the iride 8.

Thus, since the system is subject to negligible disturbance, screens 8 are eliminated, causing the guide's makeup described in the present invention to be simple. Said makeup involves several cross sections 12 (FIG. 5) in dielectric material. These cross sections are placed at equal distances d and have openings of 2a diameter, with transversals of 8' thickness and width 1. The same cross sections 12 can, generally speaking, have any shape whatever. In practice, however they should be of circular form, as cross section 12a in FIG. 6, or of rectangular form, as cross section 12b in FIG.

The present cross-sectioned iterative guide has various advantages over the conventional iride and lens dielectric guides. First, the present guide is light and takes up little space since its structure's transverse size is little more than the size of the beam. Second, the present guide's construction is markedly simple and accurate, permitting it great tolerance. This construction simplicity is due to the (12, 12a, 12b) cross sections having an 8 thickness corresponding to a rather low minimum loss for the equivalent resonator. Third, the diffraction loss due to iteration is lower than the loss suffered using guides of equally-sectioned irides, with the result that iterative guides equivalent resonators loss ratio is likewise less than that of iride guides.

The iterative guide, moreover, almost insensitive to effects caused when the cross sections 12 are not exactly parallel, presents when compared to a lens guide (FIG. 2a) much lower loss due to diffusion, reflection and scattering," since only a small part of the beams energy moves in contact across the cross sections dielectric structure.

For high-power transmission, furthennore, the conventional lens guide may offer inconveniences through damage occurring in the lenses dielectric material or through discharge during operation at the beams minimum section point between one lens and another. The present iterative guide, contrarily, does not present the first of the above inconveniences, since there is no dielectric material in correspondence with the beams central part, while the second inconvenience is reduced in the present guide due to its overall larger beam section (greater mode volume").

The present type of cross section guide also lends itself, in combination with an identical guide, to directional coupling (FIG. 8). In fact, the coupling of two parallel iterative guides can be realized by utilizing the equivalent resonators property which allows independent control of diffraction loss along each edge. In such a case, each cross section can be made up of two elementary cross sections and can be formed by a rectangular cross section with dimensions of 4a X 2a, whose transverse has 6' thickness and 1 width. The cross section has a transverse portion 130, which develops itself along the median parallel line at the main l3 cross sections shortest sides in a way to fonn two adjacent, more or less rectangular cross sections.

The transverse has a width such as to assure the coupling desired by progressively widening the section of the cross section in perpendicular planes to the axes X X in the direction of the beams propagation, and coupling can be realized using the free space, that is through the construction of wide-end-tipped antennas, such realization not being shown in the drawings.

For practical use, an iterative guide made up of 36 elements has been constructed, wherein each element consists of a quadrilateral cross section of 230 X 230 mm, in which the transverse area of the cross sections sides measures 1.4 X 1.5 mm, the cross sections being equidistanced by 320 mm, respectively. The work wavelength is 8 mm. Teflon is the dielectric material used and presents low dielectric loss. A resonator transmitter with semi-transparent reflectors and open resonators has been utilized with the aim of obtaining optimal emitting efi'iciency. The guide's measured attenuation is about 0.01 db per cell.

We claim:

1. A beam waveguide comprising in combination a plurality of frame-like elements arranged equi-spaced and coaxially along the transmission path of the beam, each frame-like element having a frame portion comprising a dielectric material and having an overall dimension only slightly exceeding the cross-section of said beam to obtain the minimum attenuation of said beam, each of said frame portions performing a phase correction equal to a phase correction produced by a step rim in an equivalent open resonator comprising plane mirrors with a step rim along the edges and spaced apart by a distance equal to that distance between adjacent frame-like elements.

2. A beam waveguide as claimed in claim 1, wherein the frame-like elements have a rectangular shape.

3. A beam waveguide as claimed in claim I, wherein the cross-sections of the frame-like elements progressively increase along the axis so that the beam waveguide functions as a horn type antenna.

4. A beam waveguide as claimed in claim 1, wherein the frame-like elements have a circular shape.

5. A beam waveguide as claimed in claim 2 electromagnetically coupled to another beam waveguide of the same type, each of said beam waveguides having a respective side adjacent the other whereby the electromagnetic field in one beam waveguide couples over the other beam waveguide in accordance with sizes of the adjacent sides.

* i K i 

1. A beam waveguide comprising in combination a plurality of frame-like elements arranged equi-spaced and coaxially along the transmission path of the beam, each frame-like element having a frame portion comprising a dielectric material and having an overall dimension only slightly exceeding the cross-section of said beam to obtain the minimum attenuation of said beam, each of said frame portions performing a phase correction equal to a phase correction produced by a step rim in an equivalent open resonator comprising plane mirrors with a step rim along the edges and spaced apart by a distance equal to that distance between adjacent frame-like elements.
 2. A beam waveguide as claimed in claim 1, wherein the frame-like elements have a rectangular shape.
 3. A beam waveguide as claimed in claim 1, wherein the cross-sections of the frame-like elements progressively increase along the axis so that the beam waveguide functions as a horn type antenna.
 4. A beam waveguide as claimed in claim 1, wherein the frame-like elements have a circular shape.
 5. A beam waveguide as claimed in claim 2 electromagnetically coupled to another beam waveguide of the same type, each of said beam waveguides having a respective side adjacent the other whereby the electromagnetic field in one beam waveguide couples over the other beam waveguide in accordance with sizes of the adjacent sides. 